[DUTCH]

As for why MB would get rid of the 3.0 V6 BT is beyond me.

It's the same thinking that refuses to bring a diesel G-Class into North America. They quite obviously have their heads firmly planted where the sun never shines.

 

[Mac]

First 3L BTC versus 2.15L BTC -- a great comparo in a common driving situation: same drive, speed, distance, time of day --i.e., my daily drive to work. It's all fwy except for getting to the fwy and from there to a parking garage. The speed was setting the cruise control for 71 (which adjusts automatically with Distronic) so human involvement was kept to a minimum as much as possible. The results: when the stars were aligned the 3L hit 28 on many occasions and just losing over the few miles after leaving the fwy. For 250BTC's first time at bat: 30.9 mpg as it sat in the parking space... >10% better mpg.

As for power, the fwy on this drive has 3 grades and the last is the steepest around in this area; and on that grade the 250BTC is running a bit under 2K RPM in 7th gear at 71 mph. The engine is just off its peak torque of 500 Nm at 1800. Referring the power curve for this engine I est. the Torque at 2K RPM to be ~483 Nm (356 lb-ft); and, the HP at 2K is right at 100 kW (134). So, the 250 BTC at that point still has a >60 law-breaking horsepower in reserve.

 

[compy223]

Great comparison, however I was expecting a bit better from the 250 engine.

It might be better in the city versus the 350

 

[Mac]

Great comparison, however I was expecting a bit better from the 250 engine.

It might be better in the city versus the 350

You can't beat that 3L BTC -- it gets 2 mpg less around town but overall its a good trade-off as it'll run with V8s -- but, MB's got a potential winner with the 2.15L as it now is the least expensive engine in the ML (GLE) lineup and runs with the gas-V6 while getting the same mpg in city driving that a 350-gasser gets on the hwy (22). By comparison, the 3L BTC was an expensive V6 and still not a V8 and diesels aren't that popular anyway so it faced a lot of headwinds, not to mention every Midsize SUV also has a 3L and it wasn't unique enough to snare the #1 spot in the comparos (Jeep won in one of them I think because it actually sounds like a diesel), despite the fact I think MB's got the best vehicle going. I think the reviewer Flavin nailed it: the "250" is brilliant; boring, but Brilliant: part of the brilliance is that MB realized 0-60 performance was not the most important factor in choosing a SUV for many of us. If you want a fast SUV off the line, the "400" won't be boring and it still gets better combined mpg than the 350-gasser; normally aspirated engines are dead meat!

 

[BillM]

I'm pretty sure the power and torque curves you are referring to are determined at full throttle. If so, unless you are pulling that last grade at full throttle you have even more in reserve than your analysis indicates.

 

[Mac]

I'm pretty sure the power and torque curves you are referring to are determined at full throttle. If so, unless you are pulling that last grade at full throttle you have even more in reserve than your analysis indicates.

Nope-- they're based on Engine Speed measured in RPMs.

I played around today with a little freewheeling on the decent of the last grade before the last climb and posted this at my destination: 31.7mph

 

[ancient aviator]

Hi all,

Personal opinion of course; reading about the first-hand reports here comparing the new 250 Bluetec in the ML vs. the ML350, I and apparently many others were led to believe the MPG would be far better than reported by 250 owners, and while this is just one consideration, I'd much rather have the ML350 Bluetec anyday. BTW, I'd gladly pay the price of the 350 vs. as stated an entry level price of the 250. Again, just a personal opinion!!

A.A.

 

[BillM]

Nope-- they're based on Engine Speed measured in RPMs.

I played around today with a little freewheeling on the decent of the last grade before the last climb and posted this at my destination: 31.7mph

Where can I find these curves?
I realize the horizontal axis is RPM and the vertical is HP or Torque. But the throttle position is very relevant. You can find different grades that can be climbed at the same road speed and gear (therefore same engine RPM) but require more or less throttle. The test curves represent the maximum torque or horsepower achievable at any given RPM.

 

[Mac]

Where can I find these curves?
I realize the horizontal axis is RPM and the vertical is HP or Torque. But the throttle position is very relevant. You can find different grades that can be climbed at the same road speed and gear (therefore same engine RPM) but require more or less throttle. The test curves represent the maximum torque or horsepower achievable at any given RPM.

For a diesel engine injecting a higher quantity of fuel into the cylinder will result in a higher power output--i.e., more RPMs, and whatever those RPMs may be you can just about climb any hill if have enough time to use a low enough gear.

For the engine we're talking about, check out the solid lines on this set of curves (Google: The Mercedes-Benz OM 651 Four-Cylinder Diesel Engine for Worldwide Use, by Peter Lückert, Dipl.-Ing, et al., 22nd Aachen Colloquium Automobile and Engine Technology 2013), as follows:

 

[Mac]

Hi all,

Personal opinion of course; reading about the first-hand reports here comparing the new 250 Bluetec in the ML vs. the ML350, I and apparently many others were led to believe the MPG would be far better than reported by 250 owners, and while this is just one consideration, I'd much rather have the ML350 Bluetec anyday. BTW, I'd gladly pay the price of the 350 vs. as stated an entry level price of the 250. Again, just a personal opinion!!

A.A.

Based on my experience, which is pretty limited at this point, and the government's posted mileage stats, the mpg for my 3L BTC were a bit overrated (especially the 28 hwy given the sort of speeds I see around here if you're in the flow of traffic) whereas for the 2.15L BTC, they're exceeding expectations so far.

 

[2008R320]

All these graphs and theoretical power to rpm ratio is my eyes a little out there, as an engineer I know why it is fun to work with the theoretical calculations, but in this case it is more down to the experience driving the car.
Biggest issue is normally the transmission, as it does not allow the drive to use the torque, it has a tendency to downshift and go into higher rpm, not like with a manual here you can really use the torque, what happens in higher rpm's on the diesel is that it looses power and I'm afraid that the 250BT more so than the 350BT, as the 250BT has a very short high torque range compared to the 350BT.
But as I have not driven the ML 250BT I can only guess (weighed in previous experience with I4 diesels)
But please report back to us how it is doing and your non-biased experience, I know that will be harder as I like MB too, so tend to look in that favor:devil

 

[Mac]

All these graphs and theoretical power to rpm ratio is my eyes a little out there, as an engineer I know why it is fun to work with the theoretical calculations, but in this case it is more down to the experience driving the car.
Biggest issue is normally the transmission, as it does not allow the drive to use the torque, it has a tendency to downshift and go into higher rpm, not like with a manual here you can really use the torque, what happens in higher rpm's on the diesel is that it looses power and I'm afraid that the 250BT more so than the 350BT, as the 250BT has a very short high torque range compared to the 350BT.
But as I have not driven the ML 250BT I can only guess (weighed in previous experience with I4 diesels)
But please report back to us how it is doing and your non-biased experience, I know that will be harder as I like MB too, so tend to look in that favor:devil

The peaky torque range caught my attention too especially given my experience with a long, flat torque curve on previous MB engines which seemed to lend itself to the feeling of power at low RPMs. Like you said, the real world test means more than what's on paper and I believe MB's 7-spd tranny is a big part of getting the most out of the I-4 biturbo diesel.

Even so, I think you'll find the torque curve pretty interesting when comparing the 250-BTC's competence to other engines. The "short" range has a lot to do with the scale that is used but check out the effective over a wider range --e.g., rather than looking at just the absolute max of 369 lb-ft (500 Nm) from 1600-1800 there also are, as follows:

• 450 Nm = 332 lb-ft Torque
1400 - 2500 RPM

• 400 Nm = 295
1250 to 3500 RPM

The latest 3.5L gas-V6 gas (302 HP @6500 RPM and 273 lb-ft Torque @ 3500-5250 RPM) maintains its highest torque of 273 over a range of 1750 RPMs. 273 lb-ft is ~370 Nm. Looking at the diesel's Torque curve, '370' appears to fall between ~1300 to 3600 RPMs which is a range of 2300 RPMs.

Acceleration requires more power but for just cruising, which takes place at the 2K-RPM range, the 250-BTC has more torque and at a lower RPM than the 5L-V8 in my old 2003 of 325 lb-ft (441 Nm) @2700-4250 RPM.

 

[BillM]

For a diesel engine injecting a higher quantity of fuel into the cylinder will result in a higher power output--i.e., more RPMs, and whatever those RPMs may be you can just about climb any hill if have enough time to use a low enough gear.

For the engine we're talking about, check out the solid lines on this set of curves (Google: The Mercedes-Benz OM 651 Four-Cylinder Diesel Engine for Worldwide Use, by Peter Lückert, Dipl.-Ing, et al., 22nd Aachen Colloquium Automobile and Engine Technology 2013), as follows:

I found that chart also. It is maximum performance - full throttle.
Forget the charts...I was only trying to make the point that you have more power in reserve than you estimated when pulling that steepest grade at 71mph. That' a good thing!

 

[Mac]

I found that chart also. It is maximum performance - full throttle.
Forget the charts...I was only trying to make the point that you have more power in reserve than you estimated when pulling that steepest grade at 71mph. That' a good thing!

I hear what you're saying but I'm no automotive engineer and obviously not savvy enough to understand why my engine is not actually generating the 100 kW needed to speed my ML up a grade at 71 mph in 7th gear at ~2000 RPM because I don't have my pedal to the metal. But, good to know.

 

[greasykid]

New ML250 BlueTEC4W

Only had for 2 weeks but getting 27mpg around town and close to 34mpg @ 65mph on freeways.


UPDATE Had to take my daughter to the airport today. 70 mi. round trip. Mostly freeway. Traveling @ normal speeds--65/70 averaged 34.0 mpg according to the on board computer. Incidentally,had my dealer take off the Michelin Latitude tires and put on the NEW Conti LX20 ECO PLUS. (255/55/18). So far great ride. Seems to handle well & really soaks up the freeway strips.Also rated 600+ on the wear scale. Did not buy these tires for longer wear but the Tirerack ratings couldn't be ignored. Better ride than the oem Michelins.

 

[ancient aviator]

Now we're talking; that's more like it...

A.A.

 

[longisland516]

Test drove the 2015 ML250 BlueTEC today. My current car is a 2014 ML350BT.

ML250BT Pros as compare to the ML350BT:
1. Around town and cruising the engine power seems ok
2. Transmission shifts smoother and seems to shift faster, does not hold gears like the ML350BT
3. Transmission is less prone to downshifting in hilly driving (could be con too)
4. Engine turbo lag seems to be less and does not have that sharp power surge
5. Start/stop seems to work very well

ML250BT Cons as compare to the ML350BT:
1. Engine has more vibration when cold (temp was around 32F)
2. Engine is much louder at idle when cold and makes somewhat more noise when warmed-up
3. Engine makes much more noise above 3k rpms at full throttle
4. Engine has more vibration at certain lower rpms ranges
5. When engine does downshift there is little additional power, this is when the car feels underpowered
6. Throttle tip-in off idle has been substantially desensitized, this may be what masks some of the turbo lag

Overall impression is that the ML250BT looses some luxury for the sake of higher mpg. Some people will find the trade off more than acceptable, but I suspect many will not. My initial thought was the 9 speed transmission would make this a viable option, but doubt the 9 speed transmission will reduce vibration at idle or noise at idle and higher rpms. In fact, I thought the 7 speed transmission paired with this engine is programmed to behave much better than in the ML350BT.

When comparing the full throttle, seat-of-the-pants feel to the ML350BT, the ML250BT feels much less powerful. I use full throttle on the ML350BT for short periods 5 or 6 times each day to and from work, so I may not be the typical driver and therefore to many people this may not matter.

 

[ancient aviator]

Nice review; good information! Thanks!

I personally would NOT opt for the 250!! I think the 350 is a great engine; however, sadly for me, my engine AND transmission issues have my car in the dealership trying to get proper service for the past 4 weeks! How sad!!

Thanks again for a great review!!

A.A.

 

[Mac]

Test drove the 2015 ML250 BlueTEC today. My current car is a 2014 ML350BT...

The review speaks well for the potential resale value of existing 3L BTCs. For new buyers the decision is, of course, not between BTCs. It's between the I-4 BTC and the petrol-3.5L V6.

Having owned both BTCs I think only those who really like 4-bangers -- which I do (most recently I've driven VW's 1.8L turbo and Chrysler's normally aspirated 2.4L Tigershark) -- can fully appreciate MB's 2.15L diesel.

I don't get the 'luxury' angle; but, for those with similar feelings MB has the GL with a 3L BTC for the nascent US diesel market.

 

[greasykid]

MY 250 BlueTEC

Have been driving MB's for over 40 yrs. This is my 7th diesel. Initial opinion;this is the smoothest of them all (diesels). Many more gassers. I can't believe I'm really driving a 4 Banger. I have no issue with the 350 BlueTEC. Just happy with my 250. Great mpg is just the frosting on the cake.